SU1724580A1 - Method of sodium tetrathioarsenate synthesis - Google Patents

Abstract

The invention relates to methods for producing sodium tetratioarsenate (V). The method is carried out as follows. Sodium disulfide is dissolved in water, and powdered realgar containing 99.3% of the basic substance is added with stirring. After 10-15 minutes, the reaction mixture is evaporated in a water bath until a yellow crystalline film forms on the surface of the solution. After cooling, the crystalline precipitate and the mother liquor are treated with alcohol, the precipitate is dried in air to constant weight. Sodium tetrathioarsenate (V) is obtained as a pale yellow substance with a yield of 98.6%. The invention allows to increase the product yield from 80 to 97.8-98.6%, to increase the content of the basic substance in it from 97 to 100%.

Description

The invention relates to chemical technology of inorganic salts, specifically to a method for producing sodium tetrathioarsenate of the formula Na3AsS4 8H20, which is used to combat agricultural pests, as well as to the starting material for the production of various inorganic compounds, including elemental sulfur.

The closest to the invention in its technical essence and the achieved result is a method for producing sodium tetratioarsenate by reacting realgar () and sulfur with sodium sulfide in an aqueous medium. For this purpose, equivalent amounts of sodium sulfide and sulfur are dissolved in a certain amount of water when heated. The resulting solution is diluted with water, then stoichiometry is added to the hot solution.

The reaction mixture is filtered, the filtrate is evaporated to form a crystalline film on the surface of the solution and cooled. The crystalline mass is sucked off and recrystallized twice from water.

The total response is as follows:

6 No. 2S-9H20 + 6S + AS4S4 4Na3AsS4 + 22H20.

The yield of the target product after double recrystallization from water does not exceed 80%. It is established that the sulfur content in the analyzed sample is 1.00–1.40% less compared to the theoretical one, although the percentage of the mouse is approximated by the composition of NaaAsS -8H20 within the limits of the analysis error. The content of the main substance in the product does not exceed 96.10%.

The main disadvantages of this method are the multistage and complexity

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process: first of all, sulfur is dissolved in a solution of sodium sulfide, then realgar, the process is carried out with heating, and the resulting reaction mixture is filtered before evaporation; low yield of the target product, namely 80% of theoretical; the low quality of the target product: the content of the basic substance in the final product is below 97%.

The aim of the invention is to simplify the process, increase the yield of the product, increase the content of the main substance in it and simplify the process.

The goal is achieved in that the method of producing sodium tetrathioarsenate by reacting a realgar with a sodium-containing compound in an aqueous medium and evaporating the reaction mass uses sodium disulfide as the sodium-containing compound, the process is carried out at room temperature, and the residue is treated with an alcohol.

The formation of the target product is explained by the following redox reaction:

AS2S2 +. 3N32S2 + 1 6N20 -

- 2№зАз54-8Н20.

For the reaction, natural realgar is used, the content of the main substance in which is 99.3%. The process of formation of the target product is completed in 10-15 minutes, after which the mother liquor is evaporated by a known method.

Distinctive features of the proposed method are the use of anhydrous sodium disulfide as a starting material instead of the corresponding sulfide and sulfur; use of freshly distilled (96%) alcohol in order to reprecipitate the target product from the mother liquor and purify the precipitated precipitate.

Example 300.3 ml (0.30 mol) of sodium disulfide was dissolved in 300 ml of water. Under stirring, 21.4 g (0.10 mol) of a powdered realgar containing 99.3% of the basic substance are added to the resulting light yellow solution with stirring. The reaction is markedly exothermic. After 10-15 minutes of stirring, the reaction mixture is evaporated in a water bath until a yellow crystalline strip forms on the surface of the solution. After cooling, the precipitated crystalline precipitate and the mother liquor is treated with 100 ml

alcohol, alcohol - the aqueous phase is decanted carefully, and the precipitate is dried in air to constant weight. 82.0 g (0.197 mol) of sodium tetratioarsenate (V) are obtained in

a pale yellow substance with a yield of 98.6%.

Found,%: As 18,17; 18.09, S 30.72; 30.67.

NasAsS4-8H20

Calculated,%: As 18.00; S 30,81.

Chemical analysis data shows that the content of the basic substance in the final product is almost 100%.

Example 2. Under the conditions described, out of 16.5 g (0.15 mol) of sodium disulfide and 10.7 g (0.05 mol) of a realgar, 40.7 g (0.098 mol) of sodium tetrathioarsenate are obtained, which is 97.8 % of theoretical.

Simplification of the process is provided by eliminating the staging of the process and filtering the reaction mixture, as well as carrying out the reaction without additional heating, increasing the yield and quality of the target product are provided by using sodium disulfide as a starting material and alcohol for final purification from impurity components.

Thus, the application of the proposed method for the preparation of sodium tetratioarsenate (V) allows the process to be significantly simplified, while the yield of the target product increases by 16–18%; The quality of the target product is significantly improved: the content of the basic substance in it is almost 100%, whereas it is not more than 97% by a known method.

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Claims (1)

Invention Formula A method for the preparation of sodium tetrathioarsenate, comprising reacting a realgar with a sodium-containing compound in aqueous solution, evaporation of the reaction mass, and crystallization of the product upon cooling, characterized in that, in order to increase the yield of the product, increase the content of the basic substance in and simplifying the process by eliminating additional heating of the reaction mass, sodium disulfide is used as the sodium-containing compound, and after crystallization of the product, the reaction mass is treated with alcohol and the product residue is dried.